Page Status: draft updated 2024-11-29
Terminologies
Page index
Introduction
The Swedish National Catalog of Organization, Offerings and Contracts is to a large extent based on coded values published as terminologies, later referred to as code systems and value sets. Code systems and value sets are used within elements of the type code. Coded values are used in many FHIR resources, e.g. Organization, Location etc. to structure the information and make it system readable. The content of code systems and value sets define a set of values in a specific context. The expression code is commonly also called term or concept and is a structured and often standardized way of expressing a value e.g. mg for milligram.
A code system / value set can represent codes from a wellknown terminology e.g. Snomed CT, or locally defined codes.
The picture below shows how the binding to code systems or value sets can be seen in a FHIR profile elements. In this case, the profile HVOBusiness has an element with a binding (1) to the value set hvo-business-category (2) which defines all valid codes for the element.
Value sets were the basepath of the URI starts with http://electronichealth.se or http://ehalsomyndigheten.se are defined by the Swedish eHealth Agency and can be fetched from the endpoint [base]/ValueSet. Value sets and code systems defined by other organisations are usually not republished by the Swedish eHealth Agency. The identity of a value set or code system can take many forms, e.g. OID, URI etc. An URI identity may in some cases be used as an URL as well, and make it possible to look up and view the concepts by a browser.
CodeableConcept and code
The way FHIR usually uses codes in resources is by defining a CodableConcept. One single concept can be described in CodableConcept by specifing one or more codes, and/or a textual description. In some cases the use of codes in the resource is very strict, e.g. in the "status" element that is available in many resources. In those cases a plain code is used.
Resource types and relations
The figure below shows how the terminology resources relate to each other.
Code System
A code system is a set of concepts where each concept has a unique code, a display name and possibly a definition of the conecept.
No code systems are published by the Swedish National Catalog of Organization, Offerings and Contracts but each value set is referring to the code system of each code in the value set.
Value Set
A value set can contain codes from more than one code system.
Some value sets contains the code OTH ("other", HL7 Nullflavor code) which represents that there is no applicable concept. In most such cases it is required to add a textual description in combination with OTH code.